The inspector will observe how the plant responds to the leak and conduct an investigation to see if there are any deficiencies in the plant's or staff's performance, said NRC spokeswoman Viktoria Mitlyng.

The plant voluntarily shut down just before 7 p.m. Tuesday because of a leak in the plant's injection/refueling water tank. The tank contained 300,000 gallons of borated water, which is used to cool the reactor when the plant's nuclear fuel is replaced or to cool the core in the event of an emergency.

The NRC was made aware of the leak in April when the plant shut down for refueling. Both Entergy and NRC inspectors monitored the leak. The plant set a limit that if more than 31 gallons leaked in a day, the plant would shut down, Mitlyng said. The plant's license specifies that no more than 34.8 gallons leak a day.

Mitlyng said the public was never at risk because of the leak: there was enough water in the tank in the case on emergency. The calculations that are used as benchmarks to shut down are "very conservative," she said.

Entergy spokesman Mark Savage declined to say when the plant may reopen. Repair work will consist of draining the tank, locating the leak, repairing the leak, refilling the tank and returning the plant to service.

Mitlyng said it will take more than one or two days to perform all of the required work.

Nuclear plants are able to operate when some parts are leaking. "There is always some kind of leakage going on," Mitlyng said. "As long as it's very small and doesn't get bigger."

But if it was any leaking of radioactive water used to generate energy, the plant would shut down immediately, Mitlyng said.